On Tuesday, the South Korean Coast Guard said it stopped two Chinese vessels that were fishing illegally, prompting about 30 other Chinese boats in the same group to swarm around and collide with the coast guard vessel.

"The safety of our own Coast Guard members was at risk," said Lee Dae-haeng, a spokesman at the Coast Guard's central regional headquarters.

No Chinese fishermen were harmed, however, said South Korea's Yonhap news agency.

China has made several diplomatic protests to South Korea over the use of force by its coast guard, said Chinese foreign ministry spokeswoman Hua Chunying.

"Using destructive weapons against fishermen can hurt them and cause great financial loss," Hua told a news briefing.

"China will strengthen the management and discipline of our fishermen. We also hope China and South Korea can increase communication on this issue."

In September, three Chinese fishermen were killed in a fire aboard their boat when a South Korean coast guard crew trying to apprehend them for illegal fishing threw flash grenades into a room where they were hiding, a South Korean official said.

(Reporting by Sue-Lin Wong in Beijing and Ju-min Park in Seoul; Editing by Clarence Fernandez)